1. Field of the Invention
The present invention relates to a transfer device which transfers a load, by sliding the load, from a first storage space to a second storage space, and preferably may be used for a stacker crane, a station for automated transfer system, and other applications.
2. Description of the Related Art
A load transfer device is mounted on a stacker crane in order to transfer a load between a rack for holding the load and the stacker crane for loading and unloading the load to and from the rack. Such a load transfer device is also used for a station at which a load is loaded to or unloaded from a transfer vehicle for automatically transferring a load. Examples of a method for transferring a load between the first storage space and the second storage space include: a fork lifting method which includes lifting a load with forks; a suction pick-up method which includes picking up a load by applying suction thereto; a pick-up belt method which includes moving a load by a pick-up belt conveyor, and a pull-up method which includes pulling up a load using a claw placed on the back side of the load.
These methods for transferring have various disadvantages. For instance, in the fork lifting method, the load needs to be moved up and down at the time of transfer, and thus a relatively large space is required in upward and downward directions of the load. As a result, such a space becomes a dead space for a rack for storing the load. In the suction pick-up method, the load is held by a suction cup, and thus a surface condition of the load is limited. In the pick-up belt method, there are many restrictions such as a load having to overhang from a rack. In the pull-up method, a difference in level between a transfer origin and a transfer destination causes damage to a load which results from being scraped at the edge of the transfer destination or collapse of a corner of the load which results from being dropped onto the transfer destination.
Examples of a method for transferring which has relatively fewer disadvantages include a clamping method (see Japanese Unexamined Patent Application Publication No. 2002-167008). The clamping method includes: inserting arms 101 into a space available at the sides or the like of a load 200 in a direction (indicated by an arrow B) opposite to a transfer direction (indicated by an arrow A), as shown in FIGS. 8A and 8B; clamping the load with the arms 101, as shown in FIG. 8C; and sliding and transferring the load by moving the arms 101 holding the load 200 in the transfer direction.
The clamping method has, for example, an advantage of completing transfer in a short time in the case where shapes of loads to be transferred are standardized.
In the clamping method, however, the level of the transfer destination is often set slightly lower than that of the transfer origin so that a load is smoothly transferred. In such a situation, it is not possible to receive, from a surface of the transfer destination, a force for supporting the load from below at the time of transferring the load from the transfer origin to the transfer destination. When a portion in contact with the load cannot support the weight of the load, a frictional force is generated between the portion in contact with the load and the load, which may result in frictional wear of or damage to the portion in contact with the load. In particular, when an elastic body such as rubber is used for the portion in contact with the load, a problem such as necessity of frequently replacing the elastic body occurs. In contrast, when a transfer device continues to support the load, it is necessary to clamp the load excessively, thereby stressing the load. Moreover, releasing the clamped load causes the entire load to fall freely, thereby damaging the load or generating a kinetic friction force on the portion in contact with the load.